(1) Field of the Invention
The present invention pertains to a surgical instrument that is constructed in an extremely small scale for use in microsurgery. In particular, the present invention pertains to a microsurgical instrument having a pair of operative surgical surfaces that are moved relative to each other in shearing or grasping procedures performed by the instrument, where the surgical instrument and its operative surgical surfaces are constructed by electric discharge machining.
(2) Description of the Related Art
Microsurgical instruments are those types of surgical instruments employed in performing surgical operations on extremely small and extremely delicate parts of the human anatomy, for example the tissues inside the human eye. There are many different types of microsurgical instruments. The more complex in construction and the most difficult to manufacture are microsurgical instruments that have at least one pair of operative surgical surfaces that move relative to each other in use of the instrument. By operative surgical surfaces what is meant is, for example, the opposed shearing surfaces of a scissors that have shearing edges that move across each other in a sheering operation performed by the instrument, or the opposed grasping surfaces of a forceps that move toward and away from each other in a grasping operation performed by the instrument. In the manufacturing of microsurgical instruments of this type, it is desirable that the scale of the instrument be as small as possible so that the introduction of the instrument to the surgical site is minimally invasive.
A typical microsurgical instrument is comprised of a manual handle that is similar in size and shape to a pen or pencil, which enables the instrument to be easily manipulated by the surgeon in one hand. An instrument head is secured to one end of the handle and the microsurgical forceps or a scissors tip projects from the instrument head. An example of this type of instrument is disclosed in U.S. Pat. No. 5,370,658, assigned to the assignee of the present invention and incorporated herein by reference.
Prior art microsurgical instrument tips of the type disclosed in the referenced patent often comprise a hollow, narrow tube projecting from the instrument head. A rod is received in the tube and the rod and tube are caused to reciprocate relative to each other in response to manual manipulation of some type of actuator on the instrument handle. The relative movement between the rod and tube operates the surgical instrument formed at the distal ends of the rod and tube. Where the surgical instrument is a forceps, the opposed jaws of the forceps are formed at the rod distal end and moving the tube over the rod or retracting the rod into the tube causes the forceps jaws to move toward each other. The reverse movements of the tube and rod cause the jaws to separate from each other. Where the surgical instrument is a scissors, one of the shear surfaces is formed at the distal end of the rod and the other shear surface is formed at the distal end of the tube. Moving the tube distal end toward the rod distal end causes the shear surfaces and their shearing edges to move toward and across each other.
As stated earlier, for microsurgical applications, the surgical instruments discussed above must be manufactured in an extremely small scale. In manufacturing the forceps discussed above, two pieces of wire stock would typically be ground down along their entire lengths until each piece was reduced to substantially half of its original thickness or width. Gripping surfaces would then be formed on the distal ends of the two pieces of wire stock by further grinding or cutting grooves across the previously ground surfaces of the wires. The two wire halves would then be welded or brazed together at their proximal ends and along an intermediate portion of their lengths. The thus formed forceps would then typically be polished.
In forming a scissors of the type discussed above, the scissor blade would first be cut from metal stock and one of the scissor blades would be welded or brazed to the distal end of the rod and the other of the scissor blades would be welded or brazed to the distal end of the tube. The operative surgical surfaces or the two shearing surfaces of the blades would then be ground forming shearing edges on the two surfaces. The rod and tube and the pair of blades attached thereto would then be polished to enhance their appearance.
The need for the final grinding step of the operative surgical surfaces of the instruments, i.e. the gripping surfaces of the forceps and the shearing surfaces of the scissors, limit the size to which a microsurgical instrument can be scaled. Due to the stresses exerted on the operative surgical surfaces of the instruments as the surfaces are ground, there must be a sufficient amount of material present in these areas of the instruments to withstand the grinding. Thus, the need to grind the material of the instrument tips to form the operative surgical surfaces of the microsurgical instruments limits the size to which the instruments can be reduced.
The present invention provides a novel method of constructing a microsurgical instrument as well as the microsurgical instrument constructed according to the method. The instrument has operative tips that are reduced in size compared to prior art microsurgical instruments. The microsurgical instrument of the invention is comprised of a handle assembly and an instrument head assembly that are basically the same as those of the prior art. However, the instrument tip is constructed according to a novel method and results in an instrument tip having a novel construction that is reduced in size from that of the prior art. Furthermore, the novel construction of the instrument tip requires fewer manufacturing steps than those of the prior art, resulting in decreased manufacturing costs.
The instrument handle and instrument head of the microsurgical instrument of the invention are basically the same as those described in U.S. Pat. No. 5,370,658, referenced earlier. Alternatively, other types of instrument handles and heads may be employed that result in relative reciprocating movement of an instrument tip rod through an instrument tip tube in response to manipulation of a manual actuator of the instrument handle by the surgeon""s hand.
The instrument handle of the invention has an elongate length with an exterior configuration that is similar to that of a pen or pencil, enabling it to be comfortably held in the surgeon""s hand. One or more lever arms are mounted on the handle exterior in positions where they can be easily manipulated by the surgeon""s fingertips. A distal end of the handle is attached to the instrument head.
The instrument head proximal end is attached to the instrument handle distal end and a microsurgical instrument tip projects from the opposite distal end of the instrument head. In the preferred embodiment of the invention, the surgical instrument tip is comprised of an elongate, narrow rod mounted in an elongate, narrow tube for relative reciprocating movement between the rod and tube. The rod and tube project from the instrument head to distal ends of the rod and tube, with the distal end of the rod extending slightly beyond the distal end of the tube. The proximal end of one of the instrument tip rod and tube is mounted stationary in the instrument head. A mechanical connection is provided between the lever arm of the handle and the other of the instrument tip rod and tube, whereby manual manipulation of the level arm produces linear reciprocating movement between the rod and tube.
In the preferred embodiment of the invention the rod is secured stationary to the instrument head and the tube reciprocates over the rod toward and away from the rod distal end. The distal end of the instrument tip rod is formed as a scissors or forceps that operates in response to the linear reciprocating movement of the tube over the rod. The novel manner in which the distal end of the rod is formed as the scissor or forceps results in a novel construction of the microsurgical instrument that is reduced in size from prior art microsurgical instruments.
Each of the microsurgical instruments of the invention is formed from a blank of metal comprising a narrow, elongate shaft with opposite proximal and distal ends and a block of metal formed at the shaft distal end. The block and the shaft of the blank are one piece of metal. In the preferred embodiment, the shaft of the blank is straight and has a center axis between its opposite proximal and distal ends. The exterior surface of the shaft is cylindrical and is dimensioned with an exterior diameter determined to enable the shaft to reciprocate linearly through the interior bore of the instrument tube without any machining or manufacturing operations required on the exterior surface of the shaft.
In preparation for forming the operative surgical surfaces in the block at the distal end of the shaft, the blank is secured in a wire electric discharge machine by mounting the shaft to the machine adjacent the proximal end of the shaft which requires no machining. A first cutting operation is then performed in the block of the one piece metal blank by moving the wire of the wire electric discharge machine and the one piece blank relative to each other. The wire is moved through the block of the blank in an elongate parabolic path that is centered relative to the shaft center axis. This separates the block into two pieces, removing a large portion of the block from the remaining parabolic shaped portion of the block left on the shaft distal end. In the next manufacturing step, the blank is rotated slightly about the shaft center axis relative to the wire and the block of the blank is cut again by moving the wire and the block relative to each other. The wire is moved through the block a second time, cutting a serrated or grooved surface into one side of the block. The blank is then rotated again about the shaft center axis relative to the wire so that it is positioned rotated 90 degrees from its original position relative to the wire of the electric discharge machine. The block of the blank is cut again by moving the wire and the block relative to each other. The wire moves through the block cutting the block into the two separate blades of the surgical scissors while also cutting a slot axially through a portion of the center of the shaft from the shaft distal end. The two scissor blades are cut with one of the blades having the plurality of the serrations or the grooves on an operative surgical surface of the blade, thereby giving this operative surgical surface a serrated edge. With the third cut performed by the wire of the wire electric discharge machine, the machining of the operative surgical surfaces of the instrument, and in particular the cutting edges of the scissors blades, is complete and no further machining operations are required, thus eliminating the grinding step required in manufacturing prior art microsurgical scissors.
The machined instrument rod is then removed from the electric discharge machine and portions of the shaft distal end that were split by the wire of the electric discharge machine are bent slightly relative to each other. The bending positions the scissor blades where they are spaced from each other, opening a gap between the cutting edges of the two blades, but where the cutting edges will move across each other as the tube of the microsurgical instrument moves over the shaft. The shaft is then assembled to the microsurgical instrument with the cutting blades and adjacent portions of the distal end of the shaft projecting from the distal end of the instrument tube.
In operation of the instrument, the tube is moved distally over the shaft causing the distal end of the tube to move the two blades of the scissors toward and across each other in the cutting operation. Reversing the movement of the tube relative to the shaft causes the distal end of the tube to move away from the bent portions of the shaft and allows the scissor blades and the split portion of the shaft distal end to move to their original bent configurations separating the scissor blades from each other.
The microsurgical forceps is constructed in a similar manner to that of the scissors. The one piece metal blank is positioned in the electric discharge machine with the blank mounted to the machine at the shaft proximal end. A first cutting step is then performed in both the block and shaft of the blank by moving the wire of the wire electric discharge machine and the blank relative to each other. The wire is moved through the block of the blank forming one of the jaws of the forceps and then the wire is moved along the center axis of the shaft at the shaft distal end. The wire is then retracted along the center axis of the shaft and moves through the block of the blank again forming the second jaw of the forceps and cutting the block into two pieces before exiting the block. As the wire of the electric discharge machine forms each jaw of the forceps, it also forms serrations or gripping grooves in the opposed operative surgical surfaces of the forceps jaws. The blank is then rotated 90 degrees relative to the wire of the electric discharge machine and the wire is again moved through the block of the one piece blank, forming each of the jaws of the forceps with a tapered tip. The serrations or grooves formed in the operative surgical surfaces of the forceps by the wire of the electric discharge machine are complete following the cutting operation of the wire and no further machining of the surfaces, i.e., grinding, is needed.
The forceps shaft is assembled to the surgical instrument in the same manner as the scissors described earlier, with the shaft extending through the interior of the instrument tube. Linear reciprocating movement of the tube over the shaft of the forceps causes the jaws of the forceps to separate from each other and to move toward each other in a gripping operation.
By manufacturing the microsurgical instruments employing electric discharge machining as described above, the operative surgical surfaces of the instruments are formed in a single step by the cutting operation of the wire of the electric discharge machine and no additional manufacturing steps, i.e. grinding of the surfaces, is needed. In this way, the surgical instruments can be constructed to a much smaller scale than prior art instruments and with fewer manufacturing steps, thus decreasing the cost of manufacturing.